Carbon black molded body and a method for producing the same

ABSTRACT

The present invention provides a carbon black molded body having different pore structure from conventional carbon black. A carbon black molded body of the present invention includes a peak M of a pore volume being exist in a specified pore diameter in the specified Log differential pore volume distribution; a specified half band width of the peak M; a specified ratio of the half band width/an area-based median diameter; and a specified difference between a maximum value and a minimum value of a Log differential pore volume.

This application is related to and claims priority under 35 U.S.C. 119to PCT international application No. PCT/JP2019/011437, filed on Mar.19, 2019, incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a carbon black molded body and a methodfor producing the carbon black molded body.

BACKGROUND ART

Carbon black is used in various fields as rubber reinforcing materialsuch as tires, coloring material such as ink and toner, conductivematerial such as magnetic tape and semiconductor components, andultraviolet absorbers. Carbon black has poor in handling andtransportability due to high dust generation and low bulk density of thecarbon black. As a solution for these problems, JPH10-140036A1 as PatentDocument 1 proposes to transport carbon black after applyingpressure-molding.

New materials using carbon black have been studied in recent years.JP2017-523024A1 as Patent Document 2 proposes as one example, a catalystcarrier using a molded body of mixture of carbon black and binder.

SUMMARY OF THE INVENTION Technical Problem

An object of the present invention is to provide novel material usingcarbon black, and more specifically, to provide a carbon black moldedbody having novel pore structure different from the pore structure ofconventional carbon black.

Solution to the Problem

The present invention solving the above problems explains below:

[1] A carbon black molded body including:

a peak M of a pore volume being exist in a pore diameter within a rangeof from 3.6 nm to 500 nm in a Log differential pore volume distribution;

a half band width of the peak M of 100 nm or less;

a ratio of the half band width/an area-based median diameter of 0.7 orless; and

a difference between a maximum value and a minimum value of a Logdifferential pore volume of 0.18 cm³/g or less in a pore diameter withina range of from 1,000 nm to 5,000 nm in the Log differential pore volumedistribution when a pore volume exists in a pore diameter within a rangeof more than 500 nm;

whereinthe Log differential pore volume distribution having a pore diameter(nm) on a horizontal axis and a pore volume (cm³/g) on a vertical axisis obtained by measuring the carbon black molded body in a pore diameterwithin a range of from 3.6 nm to 5,000 nm of the carbon black moldedbody by mercury intrusion porosimetry.

[2] The carbon black molded body according to above [1], wherein anumber of peaks of the pore volume in the Log differential pore volumedistribution in a pore diameter within a range of from 3.6 nm to 500 nmis one peak.

[3] The carbon black molded body according to above [1], wherein thecarbon black molded body has a BET specific surface area of from 10 m²/gto 2,000 m²/g.

[4] A method for preparing a carbon black molded body, including:processing a carbon black with an isostatic pressing treatment.

[5] The method for preparing a carbon black molded body according toabove [4], wherein the isostatic pressing treatment is conducted aftermixing two or more kinds of carbon black.

[6] The method for preparing a carbon black molded body according toabove [5], wherein the mixing is a composite treatment in which two ormore kinds of the carbon black are pulverized and mixed.

Advantageous Effects of the Invention

The present invention provides a new carbon black molded body havingunique pore structure. In particular, the carbon black molded body ofthe present invention has an adsorption performance for an object to beadsorbed that could not be adsorbed by conventional carbon black becausethe carbon black molded body of the present invention has different porestructure from pore structure of the conventional carbon black.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a Log differential pore volume distribution curve obtainedby a nitrogen gas adsorption method.

FIG. 2 shows a Log differential pore volume distribution curve obtainedby a nitrogen gas adsorption method.

FIG. 3 shows a Log differential pore volume distribution curve obtainedby mercury intrusion porosimetry.

FIG. 4 shows a graph plotting the relationship between a primaryparticle diameter and an area-based median diameter obtained by mercuryintrusion porosimetry.

FIGS. 5A and 5B are graphs plotting relationship between an area-basedmedian diameter and a half band width of a pore diameter distributionobtained by mercury intrusion porosimetry.

FIG. 6 shows a Log differential pore volume distribution curve obtainedby mercury intrusion porosimetry.

FIG. 7A shows a log differential pore volume distribution curve (mercuryintrusion porosimetry) of a carbon black molded body prepared by simplemixing two types of raw materials, and FIG. 7B shows a log differentialpore volume distribution curve (mercury intrusion porosimetry) of acarbon black molded body prepared by compounding two types of rawmaterials.

FIG. 8 shows a steam adsorption isotherm of a carbon black molded body.

FIG. 9 shows a Log differential pore volume distribution curve obtainedby measuring the carbon black molded bodies of Examples 4 to 6 bymercury intrusion porosimetry.

FIG. 10 shows a graph plotting the protein separation test results ofthe examples.

DESCRIPTION OF EMBODIMENTS

Carbon black has complex aggregate structure (primary aggregate)configured by branched irregular chains of spherical fine particles(primary particles) having its size of from several nm to hundreds nmare branched into irregular chains. Further, the several primaryaggregate may aggregate to form an agglomerate (secondary aggregate) byvan der Waals force or adhesion with each other. Therefore, measurementof pore size distribution of powder state carbon black counts voidsbetween primary particles in a primary aggregate, voids between primaryaggregates, voids between secondary aggregates, and other voids aspores. A pore diameter of conventionally known carbon black (unmoldedcarbon black powder, the same applies hereinafter) shows unevendistribution as shown in the pore volume distribution curve of FIG. 6(Comp. 1) because these voids are irregularly formed in the carbonblack.

The present inventors had studied carbon black to provide more uniformpore size distribution than that of conventional carbon black. Thestudies lead the inventers to the present invention that isostaticpressing treatment of carbon black makes the carbon black uniformly beconsolidated to reshape interparticle voids uniformly and thus obtainedcarbon black molded body has more uniform pore size distribution thanthat of conventional carbon black.

The carbon black molded body of the present invention satisfiesfollowing conditions (I) to (1Y) in terms of the Log differential porevolume distribution (dV/d log (D)) obtained by measuring the carbonblack molded body in a pore diameter within a range of from 3.6 nm to5,000 nm by mercury intrusion porosimetry in which a pore volumedistribution curve is plotted in a Log differential pore volumedistribution diagram having pore diameter (diameter: nm) as thehorizontal axis and pore volume (cm³/g) as the vertical axis.

(I) A peak M of a pore volume indicated by the pore volume distributioncurve exists in a pore diameter within a range of from 3.6 nm to 500 nm.

(II) A half band width of the peak M is 100 nm or less.

(III) A ratio of [the half band width/an area-based median diameter] is0.7 or less.

(IV) when a pore volume exists in a pore diameter exceeding 500 nm, adifference between a maximum value and a minimum value of a Logdifferential pore volume of 0.18 cm³/g or less in a pore diameter withina range of from 1,000 nm to 5,000 nm in the Log differential pore volumedistribution diagram.

The carbon black molded body of the present invention has unique porestructure. The present invention defines physical properties specifiedby the mercury intrusion porosimetry as an index for the pore structuralcharacteristics. The above (I) to (III) define physical propertiespeculiar to the carbon black molded body of the present invention thatthe peak M appeared in a predetermined range specified by the poredistribution curve is sharp and the carbon black molded body has anuniform pore distribution. The above (IV) is an index mainly fordifferentiating the carbon black molded body of the present inventionfrom a conventional carbon black molded body. The pore structure of thecarbon black molded body obtained by the isostatic pressing treatment asin the present invention is hard to be reconstructed. Conventionalcarbon black is unpressurized form as it is or molded by uniaxial pressmolding. Therefore, measuring the conventional carbon black by themercury intrusion porosimetry reconstructs pore structure by pressure ofmercury intrusion which results in changing the pore structure of thecarbon black molded body before and after the measurement. That is, theconventional unpressurized or the uniaxial pressed carbon black moldedbody before the measurement has different pore structure from the carbonblack molded body of the present invention in that a peak top positiondoes not overlap with each other as shown in FIG. 1 (Comps. 1 and 2).However, the measurement of the conventional carbon black by mercuryintrusion porosimetry changes its peak top position as shown in FIG. 6which may satisfy above (I) to (III). The present invention definesabove (IV) as a further index for distinguishing the carbon black moldedbody of the invention from a conventional carbon black molded body whichchanges the pore structure by pressure during the measurement. Detailreasons are explained below.

Mercury intrusion porosimetry intrudes mercury into voids between carbonblack particles when measuring carbon black. During the measurement,mercury intrusion reconstructs the voids of non-consolidated material(Comp.1) such as conventional unpressurized carbon black to indicatenearly the same pore volume distribution curve having a peak M1 withgenerally the same distribution as the carbon black molded body of thepresent invention (Ex.4) as shown in FIG. 6. As mentioned above, themeasurement of the conventional carbon black by the mercury intrusionporosimetry applies the same pressure to the voids by mercury intrusionas the pressure of the isostatic pressing treatment. Therefore,distinguishment between the carbon black molded body of the inventionand the conventional carbon black may be difficult based only on thepeak in the distribution curve. However, the conventional carbon blackhas numbers of voids having a relatively large pore diameter. Forexample, numbers of voids exist in a pore diameter of larger than thepore diameter of the distribution peak top. Therefore, the pore volumedistribution curve of the conventional carbon black tends to haveextremely enlarged vertical axis value in the pore diameter larger thanthe pore diameter of the distribution peak compared with a vertical axisvalue in the pore diameter smaller than the pore diameter of thedistribution peak value. On the other hand, the carbon black molded bodyof the present invention tends to have decreased vertical axis value ofa pore diameter as a pore diameter becomes larger than the pore diameterof the distribution peak because the carbon black molded body of thepresent invention has more uniformly formed pore diameter than that ofthe conventional carbon black molded body.

FIG. 6 shows the same tendency of the pore volume distribution curve(Comp. 2 in FIG. 6) of the carbon black molded body obtained by theuniaxial pressing (hereinafter referred to as uniaxial pressed carbonblack molded body) as that of the conventional carbon black. That is,the uniaxial pressing applies pressure to the carbon black only from onedirection and yields uneven pores having various diameters due toinsufficient pressure from the other direction. Therefore, by applyingthe mercury intrusion porosimetry to the uniaxial pressed carbon blackmolded body having the pore volume distribution curve as shown in FIG. 1(Comp.2), which is measured by the nitrogen gas adsorption method, thepores are consolidated by mercury intrusion as same as the poresconsolidated by the isostatic pressing treatment. Thus obtained uniaxialpressed carbon black molded body shows nearly the same pore volumedistribution curve having a peak M1 as the pore volume distributioncurve of the carbon black molded body of the present invention as shownin FIG. 6. Whereas, FIG. 6 confirms that the uniaxial pressed carbonblack molded body shows a pore volume distribution curve with many voids(pores) on the larger pore diameter side than the pore diameter of thedistribution peak M1 (for example, near the peak M2). Accordingly, thepresent invention defines above (Iv) as an index for distinguishing thecarbon black molded body of the invention from a conventional carbonblack molded body by considering the above mentioned changes influencedby the mercury intrusion porosimetry.

Followings explain the above indexes (I) to (IV).

(I) Peak M the Peak M Exists in a Pore Diameter within a Range of from3.6 Nm to 500 nm

The “peak” in the present invention means the maximum value of porevolume on a pore volume distribution curve of the Log differential porevolume distribution. The carbon black molded body of the presentinvention has a distribution peak M in a pore diameter of from 3.6 nm to500 nm. The peak position of the distribution curve on the horizontalaxis may be adjusted according to a method for preparing the carbonblack molded body described later. Accordingly, the distribution peakposition may be adjusted according to its application, and thedistribution peak may exist in either the mesopore region (2 nm to 50nm) or the micropore region (over 50 nm to 500 nm). Considering theselectivity for adsorbate, the position of the peak M is preferably in apore diameter of 400 nm or less, more preferably 300 nm or less, stillmore preferably 250 nm or less, further more preferably 100 nm or less,80 nm or less, 60 nm or less, 40 nm or less, and 20 nm or less in thispreferable order.

(II) Half Band Width of the Peak M: 100 nm or Less

The half band width of the peak M is from 1 nm to 100 nm or less. As thehalf band width becomes narrower, the pore diameter becomes moreuniform. This means pores having a desired pore diameter are formed moreaccurately. In addition, as the half band width becomes narrower, forexample, the adsorption property for adsorbate suitable for the desiredpore diameter is improved more. The half band width of the distributionpeak is preferably 100 nm or less, 50 nm or less, 40 nm or less, 30 nm,20 nm or less, and 10 nm in this order.

(III) A Ratio of [Half Band Width/Area-Based Median Diameter]: 0.7 orLess

The carbon black molded body of the present invention has a sharper peakand more uniform pore size distribution compared with that of aconventional carbon black molded body because the carbon black moldedbody of the present invention is subjected the isotropic pressuretreatment. The present invention defines the relationship between thehalf band width and the area-based median diameter as a ratio of “halfband width/area-based median diameter” as the index for the sharpnessand uniformity of the pore diameter distribution. The ratio of half bandwidth/area-based median diameter is 0.7 or less, preferably 0.6 or less,more preferably 0.5 or less, and preferably 0.1 or more. The half bandwidth uses the half band width of the peak M (nm). The area-based mediandiameter uses a value (nm) of the carbon black molded body measured bythe mercury intrusion porosimetry.

The area-based median diameter of the present invention means a valueobtained by measuring and calculating the pore diameter of the carbonblack molded body by the mercury intrusion porosimetry, and the detailconditions of the measurement are based on the examples of the presentinvention. If the area-based median diameter takes extremely smallvalue, the adsorption speed may be decreased. If the area-based mediandiameter takes extremely large value, the carbon black molded body maybe bulky. Accordingly, the area-based median diameter is preferably 500nm or less, more preferably 250 nm or less, and still more preferably100 nm or less.

(IV) The Difference Between the Maximum Value and the Minimum Value ofthe Log Differential Pore Volume in a Pore Diameter within a Range offrom 1,000 nm to 5,000 nm when a Pore Volume Exists in a Pore Diameterwithin a Range of More than 500 nm: 0.18 cm³/g or Less

The carbon black molded body of the present invention having moreuniform pore diameter than that of the conventional carbon black moldedbody shows a tendency of decreased amount of large pore diameters as apore diameter becomes larger than the pore diameter at the distributionpeak top. On the other hand, conventional carbon black or uniaxialpressed carbon black molded body have large difference between themaximum value and the minimum value of the Log differential pore volumein a pore diameter within a range of from 1,000 nm to 5,000 nm as shownin FIG. 6. Based on the Log differential pore volume distribution in thepresent invention, when the pore volume exists in a pore diameter withina range of more than 500 nm, the difference between the maximum valueand the minimum value of the Log differential pore volume in a porediameter within a range of from 1,000 nm to 5,000 nm is 0.18 cm³/g orless, preferably 0.1 cm³/g or less, more preferably 0.05 cm³/g or less.The lower limit of the difference is not particularly limited, and maybe 0 cm³/g.

The carbon black molded body of the present invention has physicalproperties satisfying the above (I) to (IV), and may satisfies at leastone of the following (V) to (VIII) as a preferred embodiment.

(V) A Number of Peaks of the Pore Volume in the Log Differential PoreVolume Distribution in a Pore Diameter within a Range of from 3.6 nm to500 nm: One Peak

The carbon black molded body of the present invention may have one peakor two or more of peaks having locally maximum value in addition to thedistribution peak M. In the present invention, the peak maybe describedas peak M1 showing the maximum value in the Log differential pore volumedistribution, and as decreasing peak value, the next maximum peak may bedescribed as peak M2 and sequentially described as peak M3 based on thepeak value. For improving adsorption performance and adsorption amountfor adsorbate having predetermined size, preferable number ofdistribution peak counted in a pore diameter within a range of from 3.6nm to 500 nm is one peak.

(VI) BET Specific Surface Area

The carbon black molded body preferably has a BET specific surface areaof 10 m²/g to 2,000 m²/g. The BET specific surface area is morepreferably 25 m²/g or more, further preferably 100 m²/g or more, andeven more preferably 200 m²/g or more because larger specific surfacearea improves the adsorption performance. The BET specific surface areais more preferably 1,500 m²/g or lower, further preferably 1,200 m²/g orlower, and even more preferably 1,000 m²/g or lower because extremelylarge BET specific surface area may decrease the density of the carbonblack molded body and may result in lowering the particle strength ofthe carbon black molded body. The BET specific surface area of thecarbon black molded body is measured by a nitrogen adsorption isothermwith a BET method.

(VII) Pore Volume in a Pore Diameter within a Range of from 3.6 nm to5,000 nm

Increasing the pore volume in a pore diameter of from 3.6 nm to 5,000 nmof the carbon black molded body may improves the initial adsorptionrate. However, increasing the pore volume in the above range tends todecrease the specific surface area. The pore volume in a pore diameterof from 3.6 to 5,000 nm measured by the Mercury intrusion porosimetry ispreferably 0.05 cm³/g or more, more preferably 0.1 cm³/g or more, andstill more preferably 0.2 cm³/g or more and preferably 2.0 cm³/g orless, more preferably, 1.5 cm³ g or less, still more preferably 1.0cm³/g or less.

(VIII) Amount of Acidic Surface Functional Groups, Amount of BasicSurface Functional Groups

The carbon black molded body of the present invention may adjust itshydrophilicity and its adsorption performance by appropriately adjustingthe amount of acidic surface functional groups and/or the amount ofbasic surface functional groups. For example, the amount of acidicsurface functional groups may be adjusted to 5 meq/g or less. And forexample, the amount of basic surface functional group may be adjusted to5 meq/g or less. The amount of acidic surface functional groups and theamount of basic surface functional groups are values based on themeasurement methods described in the examples.

The size of the carbon black molded body is not particularly limited,and can be appropriately selected depending on its application. Further,the shape of the carbon black molded body is not particularly limited toa specific shape.

A preferred method for producing the carbon black molded body of thepresent invention is described below.

Carbon Black

The carbon black used as a raw material can be appropriately selectedfrom the group consisting of furnace black, acetylene black, lamp black,thermal black, channel black, roller black, disk black, and other knowncarbon blacks. These examples can be used alone or in any combination.The present invention may accept various commercially available carbonblacks as a raw material. The method for producing carbon black is notparticularly limited, and any carbon black obtained by various knownproduction methods can be used in the present invention.

The present invention permits to use commercially available carbon blackas it is, therefore the carbon black has no limitation of a primaryparticle diameter, an average particle diameter, and specific surfacearea. The larger primary particle size of the carbon black increases thesize of the interparticle voids. Therefore, the present invention allowsto appropriately select a primary particle size to obtain a desired poresize. The carbon black may be in any state of primary particles, primaryaggregates, and secondary aggregates. The carbon black may be crushedand classified to obtain a desired state if necessary.

The carbon black molded body of the present invention has pores formedby voids between the carbon black particles. The carbon black moldedbody of the present invention has large adsorption capacity and capableof adsorbing large adsorbates because the pores formed by theinter-particle voids have a larger pore size and larger pore volume thanthat of the unmolded carbon black.

In the present invention, the carbon black is molded by the isostaticpressing treatment. The carbon black may be molded by the isostaticpressing treatment after pretreating the carbon black. Examples of thepretreatment include (I-1) activation treatment, (I-2) mixing treatmentor composite treatment, and (I-3) oxidation treatment. Thesepretreatments may be performed alone or in combination.

(I-1) Activation Treatment

The carbon black may be processed by the activation treatment. Theactivation treatment of the carbon: black may change pore structure andspecific surface area of the carbon black to form carbon black porestructure suitable for adsorbate. Therefore, using the activated carbonblack as a raw material improves the adsorption performance for aspecific adsorbate. Any know activation treatment such as steamactivation and alkali activation are applied as the activationtreatment.

(I-2) Mixing Treatment or Composite Treatment

The present invention allows to use several kinds of carbon black. Theseveral kinds of carbon black may be processed by simple mixingtreatment, or composite treatment as described later. The simple mixingtreatment means that several kinds of carbon black is put in the samecontainer and then stirred and mixed while adding water or otheradditive appropriately. Therefore, simple mixing treatment hardlyclashes the carbon black particles or pulverizes agglomerates of thecarbon black particles. The simple mixing treatment of the carbon blackmay not change the composition of the agglomerates. Therefore,processing thus obtained carbon black by the isostatic pressingtreatment yields carbon black molded body having a distribution peak ofeach carbon black used as a raw material as shown in FIG. 7A (Ex.10).

The composite treatment mixes several kinds of carbon black havingdifferent particle diameters and pulverize primary aggregates andsecondary aggregates into primary particles level to reconstituteaggregates. The composite treatment mixes several kinds of carbon blackat primary particle level by pulverizing aggregates or large aggregatesof the carbon black. Therefore, the aggregates of the carbon blackobtained by the composite treatment (herein after may be calledcomposite carbon black) has different aggregate structure from theaggregate structure of the carbon black mixture obtained by the simplemixing treatment because the aggregate structure of the composite carbonblack is reconstituted in combination with primary particles havingdifferent particle sizes. After the composite treatment, processing thusobtained carbon black by the isotropic pressing treatment yields moreuniformly formed voids, and thus obtained carbon black molded body has anew distribution peak different from the peak of the above carbon blackmolded body obtained from the simple mixing treated carbon black asshown in FIG. 7B (Ex.11). For example, adjustment of mixing ratio ofseveral kings of raw material carbon black having different particlesize distribution peaks allows to control distribution peak positions ofthe carbon black molded body by conducing the composite treatment. Thecomposite treatment uses preferably mechanical stirring and mixing meanssuch as a ball medium mill (such as a vibrating ball mill, a planetaryball mill), a jet mill, a wet jet mill, a wet high-speed rotary mill(such as a colloid mill), a medium stirring mill (such as a stirred tanktype bead mill, a flow tube type mill). The composite treatment may beeither a wet type process or a dry type process.

(I-3) Oxidation Treatment

The carbon black may be processed by oxidation treatment in the presentinvention. The oxidation treatment changes the amount of functionalgroups on the surface of the carbon black and thereby changes theproperties such as adsorption and hydrophobicity of the carbon blackmolded body. The oxidation treatment increases the amount of acidicfunctional groups of the carbon black and decreases the amount of basicfunctional groups. Also, the oxidation treatment of the carbon blackimproves hydrophilicity by changing the amount of surface functionalgroups. Therefore, processing the oxidized carbon black by the isostaticpressing treatment yields the carbon black molded body having improvedhydrophilicity and improved adsorption to polar molecules.

Oxidation treatment may be either wet oxidation treatment or dryoxidation treatment. As the dry oxidation treatment, for example, thecarbon black may be supplied with oxidizing gas such as air or ozoneinto a furnace heated to in the range of about 200° C. to 400° C. As thewet oxidation treatment, for example, the carbon black and an oxidantcontaining solution such as inorganic acids and/or organic acids may bestirred under in the range of 50° C. to 120° C. for 5 hours to 15 hours,followed by washing and drying. The amount of acidic functional groupsof the carbon black can be controlled by appropriately adjusting thetreatment time, treatment temperature, and other conditions.

Isostatic Pressing Treatment

The present invention molds above carbon black by isostatic pressingtreatment. The isotropic pressing treatment applies pressure equally toa carbon black surface for pressure molding without directions. Examplesof the isostatic pressing treatment includes cold isostatic pressingtreatment (CIP: Cold Isostatic Pressing), hydrostatic pressuringtreatment, rubber pressing treatment, and hot isostatic pressing (HIP:HOT Isostatic Pressing). The cold isostatic pressing treatment (CIP) ispreferable among examples because the cold isostatic pressing treatment(CIP) applies a three-dimensionally uniform pressure to a substanceunder a room temperature. The cold isostatic pressing treatment may beeither wet treatment or dry treatment. Any known pressurizing mediumsuch as gas or liquid may be used in the present invention.

The carbon black molded body consolidated by the isostatic pressuringtreatment without using a binder has enough strength to maintain itsdesired shape. Carbon black molded body obtained by applying theisostatic pressing treatment to the carbon black with binders reducessignificantly pore volume and specific surface area of thus obtainedcarbon black molded body. The present invention preferably adds nobinder to the carbon black when conducting the isostatic pressingtreatment. Therefore, the amount of binder contained in the carbon blackmolded body is preferably 20% by mass or less, more preferably 10% bymass or less, and still more preferably 0% by mass.

As the treatment pressure of the isostatic pressing treatment isincreased, the inter-particle voids decreases its void size, and thepore diameter to be formed tends to be decreased. Further, when thetreatment pressure is increased, the shape of the pore volumedistribution curve also becomes sharper with the distribution peak atthe center of the curve, that is, the pore diameter is easilyuniformized. Accordingly, the treatment pressure of the isostaticpressing treatment is preferably 20 MPa or more, more preferably 50 MPaor more, still more preferably 100 MPa or more, and even more preferably200 MPa or more. When the treatment pressure is too high, the voids tobe formed tend to be decreased. Therefore, the pressure is preferably500 MPa or less, more preferably 400 MPa or less, still more preferably300 MPa or less, and even more preferably 250 MPa or less. The pressureholding time of the treatment is preferably 1 minute or longer, morepreferably 5 minutes or longer. A longer pressure holding time saturatesthe above effects, and therefore, the pressure holding time ispreferably 60 minutes or shorter, more preferably 30 minutes or shorter.

The isotropic pressing treatment improves the strength of the carbonblack molded body and thereby the carbon black molded body suppressesdestruction of its form by friction during its handling or its use.Therefore, the carbon black molded body of the present inventionachieves higher packing density to increase the adsorption efficiency.

A post-treatment may be applied to the carbon black molded body obtainedby the above isostatic pressing treatment. Examples of thepost-treatment include (II-1) secondary molding treatment and (II-2)heat treatment. One or combination of these post-treatments may beperformed after the isostatic pressing treatment. The application orderof the post-treatment combination is not particularly limited. Inaddition, the pretreatment and the post-treatment may be performed inany combination.

(II-1) Secondary Molding Treatment

The carbon black molded body may be used as an adsorbent such as anadsorption filter as it is, crushed into a desired size or formed intodesired shape to be used as an adsorbent. The present invention includesany secondary molded body having same distribution peak as the carbonblack molded body. The carbon black molded body may take any shapeaccording to its application. The carbon black molded body may be formedinto a secondary molded body to have desired shape such as pellet shape,plate shape, briquette shape, or sphere shape according to itsapplication.

(II-2) Heat Treatment

Heat treatment may apply to the carbon black molded body. The heattreatment may change various properties of the carbon black molded bodysuch as crystallinity, oxidation resistance, surface functional groupcontent, and hydrophobicity. An increase in the heat treatmenttemperature progresses carbon black crystallization yielding anoxidation resistance improvement. Also, an increase in the heattreatment temperature reduces the amount of acidic functional groups andincreases the amount of basic functional groups. An adjustment of theamount of surface functional groups such as the ratio of the acidicfunctional group amount to the basic functional group amount changes thehydrophobicity and kinds of adsorbates.

An application of the heat treatment to the carbon black molded bodyexpands inter-particle voids size concurrently occurred with thermalshrinkage of the carbon black particles which tend to increase the porediameter and decrease the specific surface area. Accordingly, applyinghigher heat treatment temperature tends to shift the position of thedistribution peak to a direction in larger pore diameter side on thehorizontal axis. An increase in the heat treatment temperature may notchange drastically the half band width of the distribution peak. Achange of the half band width may be suppressed within plus 2 nm afterthe heat treatment compared to that of before the heat treatment.Therefore, the carbon black molded body of the present inventionmaintains the characteristic pore structure having a uniform and sharppore distribution.

The heat treatment temperature may be appropriately set according to thedesired characteristics described above. As examples, an increase in theheat treatment temperature reduces the amount of acidic functionalgroups. As specific examples, the heat treatment temperature of 1200° C.or more removes functional groups to non-detected level. Also, anincrease in the heat treatment temperature increases degree ofcrystallization of the carbon black. Therefore, the preferred heattreatment temperature is less than graphitization temperature of thecarbon black.

The carbon black molded body of the present invention has novel porestructure which is unavailable in conventional carbon black. Andadjustment of the pore structure allows the carbon black molded body toapply for various applications. The carbon black molded body of thepresent invention is usable for an adsorbent as for example because theinterparticle void functions as a pore having adsorption performance.Examples of the adsorbent includes various application such as used forliquid phase treatment such as water purification treatment, wastewatertreatment, and precious metal recovery treatment; air purificationtreatment, deodorization treatment, gas separation treatment; solventcollection treatment; and exhaust gas treatment. In addition, the carbonblack molded body of the present invention is capable of adsorbing asubstance having a size that is impossible to be adsorbed byconventional carbon black. And the carbon black molded body of theinvention is applicable in medical use as an adsorbent for variousproteins, riboproteins, viruses, macroparticles, lysozyme, and the like.

EXAMPLES

The present invention will be more specifically described below, by wayof examples. However, the present invention is not limited by thefollowing examples. It is naturally understood that modifications may beproperly made and practiced within the scope adaptable to the gistsdescribed above and below. All of these are included in the technicalscope of the present invention.

Raw Material

Molded bodies were prepared under the following conditions using the rawmaterial Nos. 1 to 5. The raw material Nos. 1 to 4 were carbon black andthe raw material No. 5 was activated carbon.

Cold Isostatic Pressing Treatment (CIP)

In Examples 1 to 11, the raw material was processed by CIP treatment.Specifically, after 3 g of the raw material was filled in a polyethylenebag and sealed, the sealed bag was loaded into a hydrostatic presspowder forming apparatus (manufactured by Nippon R & D Industries),After operating the apparatus to increase the pressure to thepredetermined pressure shown in Table 2, the CIP treatment was appliedin which the pressure was maintained for the predetermined time shown inTable 2 and then obtained a sample.

Heat Treatment at 1200° C.

In Example 5, heat treatment was further performed in a lifting furnaceafter the CIP treatment. Specifically, after the CIP treatment, about 3g of the obtained molded body was charged into a porcelain crucible, andthen the temperature was increased to 1200° C. at a rate of 4.2° C./minwhile flowing nitrogen at 2 L/min and then maintained the temperaturefor 2 hours to perform heat treatment to obtain a sample.

Heat Treatment at 2400° C.

In Example 6, heat treatment was further performed in a graphitizationfurnace (Kurata Giken Co., Ltd.). Specifically, after the CIP treatment,about 3 g of the obtained molded body was charged into a porcelaincrucible, and then the temperature was increased to 2400° C. at a rateof 10° C./min under argon atmosphere and then maintained the temperaturefor 2 hours to perform heat treatment to obtain a sample.

Example 10 Simple Mixing Treatment—CIP Processing

In this example, 5 g of the raw material 1, 5 g of the raw material 2and 100 g of pure water were put in a glass container, and wet-mixingwith a stirrer (Three One Motor manufactured by Shinto Kagaku Co., Ltd.)equipped with a stainless steel stirring blade was conducted by rotatingthe stirring blade at 500 rpm for 30 minutes at room temperature. Thusobtained suspension was dried overnight (holding temperature: 115° C.)in a box type dryer at 115° C., and then subjected to the CIP treatmentunder the same conditions as in Example 9 to obtain a sample.

Example 11 Composite Treatment—CIP Treatment

In this example, 5 g of the raw the material 1, 5 g of the raw materialthe 2, 250 g of zirconia balls (φ3 mm) and 100 g of pure water were putinto a pot (250 mL) for a planetary ball mill, and then wet pulverizedfor 30 minutes. Thus obtained suspension was dried overnight (holdingtemperature: 115° C.) with a box type dryer at 115° C., and thensubjected to the CIP treatment under the same conditions as in Example 9to obtain a sample.

In Comparative Examples 1 and 3, the raw material as it is was used as asample without any pressure treatment or other treatment.

Comparative Example 2 Uniaxial Press Treatment

In this example, 3 g of the raw material was packed in a mold forforming a cylinder shape having an inner volume of 24 mm cp, and waspressurized to 80 kN with a hydraulic hand press, and the pressure wasmaintained for 3 minutes to perform a uniaxial pressure treatment toobtain a sample.

Properties of each obtained samples were measured by the followingmeasurement methods.

Specific Surface Area

After treating 0.2 g of the sample by vacuum heating at 250° C., anitrogen adsorption isotherm was obtained under a liquid nitrogenatmosphere (77 K) using a nitrogen adsorption apparatus (“ASAP-2420”manufactured by Micromeritics Co.), and the specific surface area (m²/g)was determined by the BET method.

Analysis by Mercury Intrusion Porosimetry

Properties of the sample were measured by using a mercury porosimeter(Poresizer 9320 manufactured by Micromeritics and Poremaster GTmanufactured by Yuasa Isonics) under the condition that the physicalproperties of mercury were set to a contact angle of 140 degrees, adensity of 13.5335 g/cm³, and a surface tension of 480 dyn/cm. Thesample was measured in a range of 1.54×10⁻³ to 413.4 MPa of mercuryintrusion pressure. Based on the result, a Log differential pore volumedistribution curve was drawn in a Log differential pore volumedistribution diagram having a pore diameter (nm) on a horizontal axisand a pore volume (cm³/g) on a vertical axis. And the pore volume, thearea-based median diameter, the peak position, the half band width ofthe peak in a pore diameter within a range of from 3.6 nm to 5,000 nm(mercury intrusion pressure 0.30 MPa to 413.4 MPa) were measured. Also,the maximum value and the minimum value of the pore volume in the Logdifferential pore volume distribution diagram in a pore diameter withina range of from 1,000 nm to 5,000 nm (mercury intrusion pressure: 0.30MPa to 1.46 MPa) were measured. Table 3 shows the results.

Area-Based Median Diameter

Based the measurement results of the above mercury porosimeter, theintegrated value of 50% in area-based was defined as the mediandiameter.

Peak Position, Half Band Width of the Peak

In the Log differential pore volume distribution of the Log differentialpore volume distribution diagram having a pore diameter (nm) on ahorizontal axis and a pore volume (cm³/g) on a vertical axis drawn basedon the measurement results of the mercury porosimeter, the maximum valueon the pore diameter distribution curve was set as distribution peak M1and the pore diameter corresponding to the peak top position of the peakM1 was specified. The peak width at half height of the peak M1 from thepeak top to the base line was defined as the half band width (peak M1).If the sample has plurality of peaks, the peak position and the halfband width were similarly determined for each peak (peak M2).

Amount of Acidic Surface Functional Groups

The amount of acidic surface functional groups was measured by the Boehmmethod (the document “H. P. Boehm, Adzan. Catal, 16, 179 (1966)”describes the method in details). In particular, firstly, 50 mL ofsodium ethoxide aqueous solution (0.1 mol/L) was added to 1 g of thesample, and the mixture was stirred at 500 rpm for 2 hours, and thenleft the mixture for 24 hours. Thereafter, the mixture was furtherstirred for 30 minutes and then separated by filtration. 0.1 mol/Lhydrochloric acid was added dropwise to 25 mL of the obtained filtrate,and the volume of hydrochloric acid titer was measured when the pHreached 4.0. As a blank test, 0.1 mol/L hydrochloric acid was addeddropwise to 25 mL of the sodium ethoxide aqueous solution (0.1 mol/L),and the volume of hydrochloric acid titer was measured when the pHreached 4.0. Then, the amount of acidic functional groups (meq/g) wascalculated by the following equation (2).

[Formula]

Amount of acidic surface functional group(meq/g)=(a−b)×0.1/(S×25/50)  (2)

a: titration volume of hydrochloric acid in blank test (mL)

b: titration volume of hydrochloric acid when the sample was reacted(mL)

S: sample mass (g)

Amount of Basic Surface Functional Groups

The amount of basic surface functional groups was determined by backtitration of the measurement of acidic surface functional group amount.In particular, 50 mL of hydrochloric acid (0.1 mol/L) was added to 1 gof the sample, and the mixture was stirred at 500 rpm for 2 hours, andthen left the mixture for 24 hours. Thereafter, the mixture was furtherstirred for 30 minutes and then separated by filtration. 0.1 mol/Lsodium hydroxide was added dropwise to 25 ml of the obtained filtrate,and the volume of sodium hydroxide titer was measured when the pHreached 8.0.

As a blank test, 0.1 mol/L sodium hydroxide was added dropwise to 25 mlof the hydrochloric acid (0.1 mol/L), and the volume of sodium hydroxidetiter was measured when the pH reached 8.0. Then, the amount of thebasic surface functional groups (meq/g) was calculated by the followingformula (3).

[Formula]

Amount of basic surface functional group(meq/g)=(c−d)×0.1/(S×25/50)  (3)

c: titration volume of sodium hydroxide in blank test (mL)

d: titration volume of sodium hydroxide when the sample was reacted (mL)

S: sample mass (g)

Adsorption Test Method for Distribution of Protein (Lysozyme)

Samples of Example 4, Comparative Example 1 and Comparative Example 3were selected for the test. The sample was crushed in a mortar andshaken for 10 minutes using a rotating and tapping sieve shaker(manufactured by SIEVE FACTORY IIDA. Co., Ltd.) with a JIS standardcircular sieve (mesh size: 53 μm, 300 μm) to obtain 53 μm to 300 μmparticles, and then the particles was dried at 115° C. for 2 hours. Thedried sample was packed into a column having an inner diameter of 10 mmφ so that the column packing height became 30 mm. After allowing thesample solvent to flow sufficiently and confirming that the pH and lightabsorbance of the column inlet and that of the column outlet are equal,a protein solution (chicken egg white lysozyme manufactured by NacalaiTesque, Inc.) was passed through the column, and the eluate from thecolumn outlet was collected by a fixed amount. About 60 ml of theprotein solution was circulated so that the space velocity SV maintains13 to 14 h⁻¹. The solution collected from the column was measured forlight absorbance at 280 nm using a spectrophotometer (U-2910,manufactured by Hitachi High-Technologies Corporation) to determine abreakthrough curve. From the breakthrough curve, the protein adsorptionamount (10% breakthrough) was determined. Table 4 shows the results.

Vapor Adsorption Test

A vapor adsorption amount Measuring device (BELSORP-max, manufactured byMicrotrap Bell) was used for the test. About 40 mg of the sample was putinto a cell, and pretreatment was performed by heating at 250° C. for 5hours under vacuum, followed by introduction of a replacement gas andthen weighing the sample. The measurement of the vapor adsorption amountwas performed in a water bath maintained at 25° C. by a circulatingthermostat within a relative pressure (P/P₀) of 0.0 to 0.85. The testwas performed on Example 4 and Comparative Example 1. FIG. 8 shows theresults.

TABLE 1 primary particle raw material No. name of raw material diameterraw material 1 Carbon black (#2650); 13 nm Mitsubishi ChemicalCorporation raw material 2 Carbon blak (MOGUL); 24 nm Cabot Corporationraw material 3 Carbon blak (MONARCH); 13 nm Cabot Corporation rawmaterial 4 Carbon black (#10); 75 nm Mitsubishi Chemical Corporation rawmaterial 5 Activated carbon (W10-30 MC — Evolve Technologies Corporation

TABLE 2 nitrogen gas adsorption primary method particle post-treatmentBET specific diameter heat surface area No. Examples types raw materialnm pressure condition treatment m^(z)/g Ex. 1 Example 1 CB-CIP rawmaterial 1 13 CIP  20 MPa-5 min — 353 Ex. 2 Example 2 CIP  50 MPa-5 min— 348 Ex. 3 Example 3 CIP 100 MPa-5 min — 362 Ex. 4 Example 4 CIP 200MPa-5 min — 341 Ex. 5 Example 5 CIP 200 MPa-5 min 1200° C. 304 Ex. 6Example 6 CIP 200 MPa-5 min 2400° C. 164 Ex. 7 Example 7 raw material 313 CIP 200 MPa-5 min — 622 Ex. 8 Example 8 raw material 2 24 CIP 200MPa-5 min — 142 Ex. 9 Example 9 raw material 4 75 CIP 200 MPa-5 min — 29Ex. 10 Example 10 raw material 1, 2 19 CIP 200 MPa-5 min — 240 Ex. 11Example 11 raw material 1, 2 19 CIP 200 MPa-5 min — 240 Comp. 1Comparative CB raw material 1 13 non — — 333 Example 1 Comp. 2Comparative CB-uniaxial raw material 1 13 uniaxial 178 MPa-3 min — 354Example 2 press molding press Comp. 3 Comparative Activated raw material5 — non — — 1121 Example 3 Carbon

TABLE 3 mercury porosimetry half band width/ pore volume area-basedarea-based of from 3 to median pore size half band width median diameter5,000 nm diameter peak M1 peak M2 peak M1 peak M2 peak M1 peak M2 No.Examples cm³/g nm nm nm nm nm — — Ex. 1 Example 1 0.52 7.3 7.1 — 2.7 —0.37 — Ex. 2 Example 2 0.43 7.0 6.7 — 2.7 — 0.39 — Ex. 3 Example 3 0.397.0 6.7 — 2.6 — 0.37 — Ex. 4 Example 4 0.33 6.5 6.4 — 2.4 — 0.37 — Ex. 5Example 5 0.36 8.0 8.0 — 2.5 — 0.31 — Ex. 6 Example 6 0.25 8.5 8.5 — 2.6— 0.30 — Ex. 7 Example 7 0.53 5.8 5.7 — 3.0 — 0.52 — Ex. 8 Example 80.47 18.4 18.6 — 6.5 — 0.35 — Ex. 9 Example 9 0.76 96.7 97.3 — 30.8 —0.32 — Ex. 10 Example 10 0.45 8.2 7.3  19 2.8 7.4 0.38 0.40 Ex. 11Example 11 0.33 9.3 9.0 — 3.9 — 0.41 — Comp. 1 Comparative 2.30 7.4 7.19936 2.5 401377 0.34 40.4  Example 1 Comp. 2 Comparative 0.70 7.0 6.7 712 2.7 2445 0.38 3.43 Example 2 Comp. 3 Comparative — — — — — — — —Example 3 mercury porosimetry pore volume in Log differential porevolume distribution in pore diameter of from 1,000 to 5,000 nm surfacefunctional group Δ [1] − [2] acidic basic [1] [2] Difference betweensurface surface total Maximum Minimum maximum value and functionalfunctional functional value value minimum value groups groups groups No.Examples cm³/g cm³/g cm³/g meq/g meq/g meq/g Ex. 1 Example 1 0.01 0.000.01 0.61 0.00 0.61 Ex. 2 Example 2 0.01 0.00 0.01 0.61 0.00 0.61 Ex. 3Example 3 0.01 0.00 0.01 0.61 0.00 0.61 Ex. 4 Example 4 0.01 0.01 0.000.61 0.00 0.61 Ex. 5 Example 5 0.00 0.00 0.00 0.00 0.21 0.21 Ex. 6Example 6 0.00 0.00 0.00 0.00 — 0.00 Ex. 7 Example 7 0.01 0.00 0.01 1.270.00 1.27 Ex. 8 Example 8 0.02 0.00 0.01 0.51 0.00 0.51 Ex. 9 Example 90.18 0.16 0.02 0.04 0.00 0.04 Ex. 10 Example 10 0.04 0.01 0.03 0.56 0.000.56 Ex. 11 Example 11 0.01 0.00 0.01 0.56 0.00 0.56 Comp. 1 Comparative1.86 1.23 0.63 0.61 0.00 0.61 Example 1 Comp. 2 Comparative 0.26 0.070.19 0.61 0.00 0.61 Example 2 Comp. 3 Comparative — — — 0.13 0.39 0.52Example 3 ※[−] in basic surface functional groups of Ex. 6 sntands meansunmeasured

TABLE 4 particle nitrogen gas adsorption method CIP condition size BETspecific pore (pressure - adjusted※ surface area volume Examples typesraw material retention time) μm m²/g cm³/g Example 4 CB-CIP raw material1 200 MPa-5 min 53~300 341 0.44 Comparative CB raw material 1 — — 3330.45 Example 1 Comparative Activated raw material 5 — 53~300 1106 0.52Example 3 Carbon surface functional group adsorption test nitrogen gasadsorption method acidic basic result for average surface surface totaldistribution pore functional functional functional lysozyme diametergroups groups groups (10% breakthrough) Examples nm meq/g meq/g meq/gmg/cm³ Example 4 5.33 0.61 0.00 0.61 7.3 Comparative 6.07 0.61 0.00 0.612.7 Example 1 Comparative 1.47 0.13 0.39 0.52 1.0 Example 3 ※Theparticle size adjustment is a classification condition of adsorptiontest for distribution of lysozyme.

FIG. 1 shows a Log differential pore volume distribution curve of eachsample measured by a nitrogen gas adsorption method. Unlike the mercuryintrusion porosimetry, the nitrogen gas adsorption method changes nopore structure by the pressure to the gap during the measurement, andthus the distribution curve reflects the pore structure of the carbonblack molded body of the comparative example as it is. Compared withExamples 1 to 4, 8, 10 and 11 conducted the isostatic pressingtreatment, Comparative Example 1 without pressure treatment had no peaksand showed non-uniform pore diameter distribution because ComparativeExample 1 was prepared without any pressure treatment. The carbon blackof Comparative Example 2 was prepared by the uniaxial press molding.This carbon black contains various pore diameters because the carbonblack was unevenly compressed from only one direction.

As shown in FIG. 1, the results of Examples 1 to 4, in which only thepressure condition of CUP treatment was changed, indicate that thedistribution peak top position tends to appear in the smaller porediameter direction as the pressure increases during the molding. It isconsidered from the results that the higher pressure during the moldingdecreases inter-particle voids to reduce pore diameter formed in themolded body

FIG. 2 shows the Log differential pore volume distribution curve of eachsample measured by the nitrogen gas adsorption method. The results ofExamples 4, 8, 10, and 11, in which the isostatic pressing treatment wasperformed under the same conditions except the raw material, indicatethat the peak M of the distribution appeared differently according tothe raw material used. On the other hand, Comparative Example 1 withoutany pressure treatment showed no peak of the distribution becauseComparative Example 1 was prepared without pressure molding. Theseresults indicate that a peak of the distribution is formed by isostaticpressing treatment.

FIG. 3 shows the Log differential pore volume distribution curves of thesamples of Examples 4 and 7 to 10 measured by the mercury intrusionporosimetry measurement. These samples were prepared by processing thecarbon black having different primary particle diameters by theisotropic pressure treatment under the same conditions. FIG. 3 clearlyindicates that the inter-particle void tends to form larger void as theprimary particle has the larger diameter. FIG. 4 shows the relationshipbetween the area-based median diameter and the primary particlediameter; FIG. 5A shows the relationship between the half band width ofthe pore diameter distribution and the area-based median diameter; andFIG. 5B shows the relationship between the ratio of [half bandwidth/area-based median diameter] and the area-based median diameter.FIG. 4 indicates that the pore diameter tends to be large as the primaryparticle has the larger diameter. Also, FIG. 5A indicates that the poredistribution tends to be broad as the area-based median diameter islarger. FIG. 5B indicates that the peak M1 has a narrow half band widthregardless of the value of the area-based median diameter whichindicates the peak M1 is sharp.

FIGS. 7A and 7B show the Log differential pore volume distributioncurves obtained by measuring Examples 4, 8, 10, and 11 by the nitrogengas adsorption method. As shown in FIGS. 7A and 7B, Example 10 in whichtwo types of carbon black (raw material Nos. 1 and 2) were processed bysimple mixing treatment showed two peak tops. Each peak of the Example10 showed the same position as the peak of Example 4 (raw materialNo. 1) and the peak of Example 8 (raw material No. 2). That is, thesimple mixing reflects the peak of each raw material as it is. On theother hand, the composite treatment disintegrates the aggregates andremixed at the primary particle level to reconstitutes aggregates inExample 11. Therefore, processing several kinds of the raw material withthe composite treatment provides the carbon black molded body having amore uniform monodisperse distribution peak, and the composite treatmentis effective for controlling pores.

FIG. 8 shows the results of examining the water vapor adsorption amountsof Example 4 and Comparative Example 1. Example 4 had smaller amount ofthe acidic functional groups than that of Comparative Example 1. FIG. 8indicates Example 4 was excellent in the water vapor adsorption andExample 4 drastically increases the water vapor adsorption amount withinthe relative pressure P/P₀ of from 0.8 to 0.85.

FIG. 9 shows the results of examining the effect of the heat treatmentand the heating temperature. FIG. 9 indicates that the pore diametertends to be large as the heat treatment of the carbon black molded bodyemploys higher temperatures. Table 3 indicates that the heat treatmentdecreases the specific surface area and increases area based mediandiameter, but hardly affects the half band width M1 of the peak. Theseresults showed the interparticle voids become large as the carbon blackparticles is shrinked by the heat treatment which resulted in shiftingthe pore volume distribution curve to the pore diameter larger side.However, it is considered that the half band width of the peak ismaintained because the pore structure is maintained.

As shown in FIG. 10, Example 4 showed a higher lysozyme adsorption ratethan Comparative Example 1 without the isotropic pressing treatment andComparative Example 3 which was the activated carbon. The resultsindicate that processing the carbon black by the isostatic pressingtreatment forms pores suitable for lysozyme adsorption to haveappropriate pore size distribution for the adsorption of the lysozyme.

1-3. (canceled)
 4. (canceled)
 5. A method for preparing a carbon blackmolded body, comprising: processing a carbon black with an isostaticpressing treatment, wherein the isostatic pressing treatment isconducted after mixing two or more kinds of carbon black.
 6. The methodfor preparing a carbon black molded body according to claim 5, whereinthe mixing is a composite treatment in which two or more kinds of thecarbon black are pulverized and mixed.